Hello, igorpec. I tried the Armbian 5.05 Debian on OPI-PC. Here are the bugs I found.
1. The auto mount of USB drive is not working, I installed usbmount package then it auto mount but cannot eject, also some filename cannot recognize and shows as ??.
2. The eject or umount of USB drive is not working, says no permission.
3. The HW decode of video using MPV is not working. B.t.w., the MPV preinstalled is old which is 0.6.6 while the newest is 0.16, the libvdpau-sunxi installs fine but not work properly.
4. The Mali400 driver seems to work, but no libmali.so and libEGL.so in /usr/lib, so I compiled from source.
5. Booting takes a long time even after configured the board type and created user account. Booting time is way slower than the 3.4.39 kernel. It will pause about a minute to boot after pressing reboot.

6. Reboot or shutdown will get black screen and logout and login then reboot or shutdown.
My suggestion: why not use the LXDE desktop as default release? It focus on the perfomance not looks.

Thank you for update. I must say I didn't notice all those problems - if you came to 5.05 with an upgrade, than this could explain the troubles.

1. - 2. Never even tested this. I guess it must be something with permissions.
3. Strange. It was working for me - playing mkv HD movie was working out of the box - "click and play".
4. I only executed es2gears ...
5. Again. It's working normally for me. I guess your board was not recognized properly. People reported that ... and if it's not, than such things are very likely - some driver / service hangs and default timeout is one minute.
6. Known issues. Don't have a solution yet.

We got enough performance for XFCE, but things has to be fixed. I hate to switch to yet another desktop and start all over again without making some real progress.

3. You're upgrading from older images, yes? We don't yet have mpv or such in the repos, we just manually inject those packages in the image. If you instead used the whole image you'd notice there's mpv 0.16 I built from git.
4. The mali-libraries are in /usr/lib/mali. Again, if you use the images there shouldn't be anything you need to do to have working GLES.

As for using LXDE: I already made a change to the images to disable compositing in xfwm4 by default -- that is one enormous CPU-hog and disabling it should improve performance nicely. Again, this change appears only in the 5.05 - image, not when you're just upgrading. You could also install kde-window-manager and use kwin_gles instead if you'd like GLES-accelerated WM with compositing and all the goodies. Try disabling compositing, use kwin_gles or try the 5.05 - image and you should see there's really no need to switch to another DE.